3GPP includes mechanisms for radio interworking between 3GPP and WLAN. The interworking improves operator control over how a user equipment (UE) performs access selection and traffic steering between 3GPP and WLANs that belong to the operator or the operator's partners. In some scenarios, the interworking may be used with other, non-operator WLANs as well.
The term 3GPP signal, as used herein, may refer to a signal transmitted by a radio network node belonging to 3GPP radio access technology (RAT) (e.g. LTE, HSPA, GSM, etc.). The term may also refer to the quality of such a signal.
The term WLAN signal, as used herein, may refer to a signal transmitted by a radio network node belonging to WLAN (e.g., 802.11 access point (AP), etc.). The term may also refer to the quality of such a signal.
3GPP/WLAN interworking may include various mechanisms for interworking. One example is network assisted (or threshold based) interworking. Another example may be referred to as network controlled interworking.
In network assisted interworking, the 3GPP radio access network (RAN) provides parameters that assist the UE with access selection and traffic steering. The RAN assistance parameters include three main components: threshold values, offloading preference indicator (OPI), and WLAN identifiers. The UE also receives RAN rules/policies that may use the assistance parameters.
For example, the threshold values may include 3GPP signal related metrics such as reference signal received power (RSRP), reference signal received quality (RSRQ), received signal code power (RSCP), or energy per chip/noise spectral density ratio (Ec/No), etc., and WLAN signal related metrics such as received channel power indicator (RCPI), received signal strength indication RSSI, WLAN load/utilization, WLAN backhaul load/capacity, etc. An example of a RAN rule that uses the threshold value is a rule that specifies that a UE should connect to a WLAN if a 3GPP signal level is below a signaled 3GPP signal level threshold at the same time as a WLAN signal level is above a signaled WLAN signal level threshold. Similarly, another rule may use thresholds to determine when a UE should steer traffic back from WLAN to 3GPP. An example algorithm may be expressed with the following pseudo code.
if (3GPP signal < threshold1) && (WLAN signal > threshold2) {   steerTrafficToWLAN( );} else if (3GPP signal > threshold3) || (WLAN signal < threshold4) {   steerTrafficTo3gpp( );}
In this interworking mechanism, it may not be feasible or desirable for the UE to consider any possible WLAN when deciding where to steer traffic. For example, an operator may not find it feasible that the UE uses this interworking mechanism to steer traffic to a WLAN that does not belong to the operator. Thus, one option is that the 3GPP RAN may send a list of WLAN identifiers to the UE, and the UE may apply the interworking mechanism only to the listed WLANs.
The 3GPP RAN may provide additional parameters used for Access Network Discovery and Selection Function (ANDSF) policies. One parameter is an offloading preference indicator (OPI). In one example, the OPI is compared to a threshold in the ANDSF policy to trigger various actions. In another example, OPI is used as a pointer to select various parts of the ANDSF policy which would then be used by the UE.
The RAN assistance parameters (e.g., thresholds, WLAN identifiers, OPI) provided by 3GPP RAN may be communicated with dedicated signaling and/or broadcast signaling. The 3GPP RAN may only send dedicated parameters to the UE when the UE has a valid radio resource control (RRC) connection to the 3GPP RAN. A UE that has received dedicated parameters may apply the dedicated parameters; otherwise, the UE may apply the broadcast parameters.
If no RRC connection is established between the UE and the 3GPP RAN, the UE cannot receive dedicated parameters. When an RRC connection has been terminated, however, a UE may apply dedicated parameters previously received from the 3GPP RAN. For example, when entering RRC_IDLE mode in LTE (or when entering idle mode, URA_PCH, or CELL_PCH in UMTS) the UE may continue to apply dedicated RAN assistance parameters for some amount of time. After the timer has expired, the UE may discard the dedicated parameters and apply broadcast parameters.
ANDSF may use the thresholds and OPI parameters communicated by the 3GPP RAN to a UE. If ANDSF policies are provided to the UE, then the UE may use the ANDSF policies instead of the 3GPP RAN rules/policies (i.e. ANDSF takes precedence).
In network controlled interworking, the 3GPP network fully controls the interworking mechanism. The 3GPP network configures the UE to send measurement reports related to WLANs the UE has discovered (or for WLANs that satisfy certain conditions). The network, based on the measurement reports, decides whether the UE should steer traffic towards one of the reported WLANs. If the UE should steer traffic towards a WLAN, the 3GPP network sends a traffic steering command to the UE.
For example, traffic steering for UEs in RRC CONNECTED/CELL_DCH state may be controlled by the 3GPP network using dedicated traffic steering commands, potentially based also on WLAN measurements (reported by the UE). UEs in IDLE mode and CELL_FACH, CELL_PCH and URA_PCH states may use a mechanism similar to the threshold based approach described above. Alternatively, UEs in these RRC states may be configured to connect to the 3GPP RAN and wait for dedicated traffic steering commands.
FIG. 1 illustrates example traffic steering steps for UEs in a connected state. FIG. 1 illustrates communications between a UE in RRC CONNECTED/CELL_DCH state and an eNodeB or Radio Network Controller (RNC).
Step 1 may be referred to as measurement control. As part of measurement control, the eNodeB/RNC configures the UE measurement procedures, which includes the identity of a target WLAN to measure.
Step 2 may be referred to as measurement report. As part of measurement report, the UE is triggered to send a measurement report according the rules specified as part of measurement control.
Step 3 may be referred to as traffic steering. As part of traffic steering, the eNodeB/RNC sends a steering command message to the UE to perform the traffic steering based on the reported measurements and traffic loading in the RAN.
For measurement control, examples of information that the UE can be configured to measure include: (1) events that trigger reporting; (2) target identifiers; and (3) types of measurements to report.
Events that trigger reporting may include: (1) a WLAN measurement goes above a threshold (possibly triggering traffic steering to the WLAN); (2) a WLAN measurement goes below a threshold (possibly triggering traffic steering away from the WLAN); (3) a 3GPP cell's radio quality goes below a first threshold and a WLAN's radio quality goes above a second threshold (possibly triggering traffic steering to the WLAN); and (4) a WLAN's radio quality goes below a first threshold and a 3GPP cell's radio quality goes above a second threshold (possibly triggering traffic steering away from the WLAN).
Target identifiers may indicate to a UE which WLANs to measure. Target identifiers may include the WLAN ID and particular operating channels to measure. Examples of target identifiers are included in the following table.
AvailabilityIdentifierDescriptionin WLANBSSIDBasic Service Set Identifier: ForBeaconinfrastructure BSS, the BSSID is theor ProbeMAC address of the wireless accessResponsepoint.SSIDService Set Identifier: The SSID may beBeaconused in multiple, possibly overlapping,or ProbeBSSs.ResponseHESSIDHomogeneous Extended Service SetBeaconIdentifier: A MAC address whose valueor Probemay be configured by a HotspotResponseOperator with the same value as the(802.11)BSSID of one of the APs in the network.All APs in the wireless network shall beconfigured with the same HESSIDvalue.Domain NameDomain Name List: element provides aANQPListlist of one or more domain names of the(HS 2.0)entity operating the WLAN accessnetwork.OperatingIndication of the target WLANN/Aclass,frequency. See Annex E of 802.11 forchanneldefinitions of the different operatingnumberclassesIf the information in the table above is not available in eNB/RNC, the RAN may configure general WLAN measurements.
Examples of measurement reports are included in the following table.
AvailabilityIdentifierDescriptionin WLANRCPIReceived Channel Power Indicator: MeasureMeasurementof the received RF power in the selectedchannel for a received frame in the rangeof −110 to 0 dBm.RSNIReceived Signal to Noise Indicator: AnMeasurementindication of the signal to noise plusinterference ratio of a received IEEE 802.11frame.Defined by the ratio of the received signalpower (RCPI-ANPI) to the noise plusinterference power (ANPI) in steps of 0.5 dBin the range from −10 dB to +117 dB.RSSIReceived Signal Strength Indicator:Measurementindication of the total RF power beingreceived.BSS LoadDomain Name List: element provides a listBeaconof one or more domain names of the entityor Probeoperating the WLAN access network.Response(802.11k)WANIndication of the target WLAN frequency.ANQPMetricsSee Annex E of 802.11 for definitions of the(HS 2.0)different operating classes
Traffic steering may include routing traffic. For the 3GPP RAN to control traffic routing (if supported) if ANDSF is not used, the 3GPP RAN needs to know which access point names (APNs) and bearers may be offloaded and which may not. The 3GPP RAN also needs a mechanism to inform the UE accordingly, so that the UE can, for example, issue a corresponding binding update with the core network (CN) over S2c. This can impact signaling between CN and eNodeB as well as the UE behavior between the access stratum (AS) and the non-access stratum (NAS). Examples of traffic to steer to or from the WLAN may include: (1) data radio bearer (DRB)/radio bearer ID (RB-ID) (i.e., the identity of a radio bearer); and (2) quality of service class identifier (QCI).
In the network assisted interworking, the 3GPP RAN indicates a set of possible WLAN identifiers that a UE should consider and the UE applies RAN rules to that set of WLANs. Similarly, in network controlled interworking the 3GPP RAN may configure a UE with a list of WLAN identifiers that the UE should measure, and the UE will report when measurement triggering conditions are satisfied for any of the WLANs identified in the list.
The WLAN includes its own mechanisms for handing over between various WLAN access points. The handover may be based on load or mobility reasons within the WLAN. A particular problem is that the WLAN steering mechanisms may conflict with the 3GPP RAN steering mechanism can result in a UE ping-ponging between WLAN access points.
For example, the 3GPP RAN may provide a UE with a WLAN identifier list that contains WLAN AP1 (e.g., AP1 has the same SSID/HESSID as one of the entries in the WLAN identifier list, or its BSSID is explicitly indicated in the list). AP2 is not in the WLAN identifier list. At some time, the UE steers its traffic to AP1 (e.g., either the conditions for the RAN rules are satisfied in network assisted interworking, or an explicit traffic steering command is received in network controlled interworking). The UE then travels into the coverage area of AP2 and the WLAN handover mechanism transfers the UE to AP2. At this point, the 3GPP RAN steering mechanism may force the UE to connect to AP1 again if the conditions for steering are satisfied. Or the UE may send a measurement report that includes only AP1, and the 3GPP RAN may send a command to steer traffic to AP1 again. After the UE returns to AP1, the WLAN mechanism may trigger the handover to AP2 again. The handover between AP1 and AP2 may continue indefinitely, resulting in a ping-pong effect.